Sweet spot matching: A thin-layer chromatography-based countercurrent solvent system selection strategy

Abstract

TLC-based strategies were proposed in 1979 (Hostettmann et al.) and 2005 (Friesen & Pauli; GUESS method) to minimize the number of partitioning experiments required for countercurrent separation (CCS) solvent system selection. As semi-empirical approaches, both proposed that the K values defining the sweet spot of optimal CCS corresponded to a matching Rf value range from the silica gel TLC plate developed in the organic phase of a biphasic or a corresponding monophasic solvent system. Despite their simplicity, there has been an absence of theoretical support and a deficiency of reported experimental evidence. The present study explores the theory required to develop correlations between Rf and K. All theoretical models surmise that the optimal Rf value range should be centered at 0.5. In order to validate the feasibility of the concept of matching Rf and K values, 43 natural products and six solvent system families were investigated. Out of 62 correlations, 45 resulted in matched Rf and K values. Based on this study, practical guidelines for the TLC-based prediction strategy are provided. These approaches will equip CCS users with an updated understanding of how to apply the TLC-based solvent system selection strategy to accelerate a targeted selection of CCS conditions.

Continuous separation of maslinic and oleanolic acids from olive pulp by high‐speed countercurrent chromatography with elution‐extrusion mode

“…A suitable solvent system could provide a proper range of partition coefficient (K D ) for target compounds. Usually, this suitable range is considered as 0.5≤K D ≤2.0 . If the K D value is too small, this will cause the compound to be eluted close to the solvent front with poor resolution; while it requires a long‐running time and a large volume of solvent as a result of the too high K D value .…”

Evidence for Chemopreventive and Resilience Activity of Licorice: Glycyrrhiza Glabra and G. Inflata Extracts Modulate Estrogen Metabolism in ACI Rats

“…The crude LicA sample, enriched from GI (eLicA, purity of LicA, ~ 50%) was a gift to SNC from Qinghai Lake Medicinal CO., Ltd. A loss-free countercurrent separation was implemented for the purification of LicA from the eLicA, as follows: TLC-based solvent system strategy (23) was performed for screening a proper solvent system. Among screened solvent systems (Supplementary Table S1), LicA was eluted by the organic phase of n - h exane- e thyl acetate- m ethanol- wat er (HEMWat, 4:6:5:5, v/v) to R f = 0.43 on a pre-coating normal-phase Si TLC plate (MACHEREY-NAGEL, Bethlehem, PA, USA).…”

Selective Depletion and Enrichment of Constituents in “Curcumin” and Other Curcuma longa Preparations

“…Subsequently, during this work, this SS was modified slightly in order to optimize separation parameters such as stationary phase volume retention. 17 Recently, a centrifugal partition centrifugation separation of 1 - 3 has been described with a heptane/CHCl 3 /MeOH/water SS. 18 The only other publication dealing with the separation of curcuminoids with CCS used pH zone refining, which introduced pH changes that foster the degradation of curcuminoids and other metabolites.…”